Field of the Invention
Embodiments of the present invention relate to a field for producing hydrogen in which hydrogen is generated by using high temperature steam electrolysis.
Related Art
Realization of a hydrogen energy society using hydrogen as an energy medium has attracted attention. As one of technology for producing hydrogen, a high temperature steam electrolysis is widely known. The high temperature steam electrolysis is a method in which hydrogen and oxygen are generated by electrolyzing steam with a high temperature (normally, 500° C. or more).
The method can advantageously reduce an amount of electricity required for electrolysis by electrolyzing steam under a high temperature environment.
To be more specific, a hydrogen electrode and an oxygen electrode are provided on both sides of a solid oxide electrolyte to constitute an electrolytic cell. High temperature steam is supplied to the hydrogen electrode side, and an electrolytic voltage is applied to the both electrodes, so that the steam is decomposed into hydrogen and oxygen.
Also, by supplying hydrogen and oxygen to a hydrogen electrode and an oxygen electrode of an electrolytic cell, respectively, and reacting hydrogen and oxygen, a reverse reaction of the high temperature steam electrolysis (a fuel cell reaction) takes place, so that electric power can be generated.
Conventionally, various apparatus configurations for achieving high durability and highly-efficient hydrogen production, such as a configuration for suppressing a gas leak between both electrodes, have been disclosed for the electrolytic cell that performs the high temperature steam electrolysis (for example, Japanese Patent Laid-Open Nos. 1994-173053 and 2007-314833).
In a hydrogen station that produces and stores a large volume of hydrogen, the high temperature steam electrolysis is performed in the reaction containment where a plurality of cell stacks in each of which a plurality of electrolytic cells are stacked are arranged. In this case, it is necessary to evenly perform an electrolytic reaction in each of the arranged cell stacks in order to obtain higher hydrogen production efficiency.
However, as the number of the arranged cell stacks is increased, the reaction containment becomes large, and a configuration inside the containment becomes complicated. Therefore, it becomes difficult to supply steam used for the electrolytic reaction to uniformly flow into each of the cell stacks. If the steam to be supplied into each of the cell stacks does not keep uniform, the electrolytic reactions are not evenly performed in the cell stacks, and the hydrogen production efficiency is lowered.
If flow rates of the steam flowing into the cell stacks become uneven, and the steam becomes deficient (steam starvation state) in some of the cell stacks, the electrolytic reaction cannot be stably continued, and the electrolytic cell may be damaged.